Hydrogen-Chlorine Fuel Cell
Hydrogen-Chlorine Fuel Cell
Where do we go from here?
Selected Publications
Literature References
A Novel Fuel Cell with Potential Applications in Carbon Sequestration and Power Grid Load Leveling
The electrical grid lacks storage capacity. Power generation equipment needs to be sped up and slowed down to exactly meet demand on a minute-by-minute basis. The amount of power-generating equipment that needs to be hooked up to the grid is the amount that can deliver just enough power for the peak-demand hour in the middle of the afternoon of the hottest day of the summer. The rest of the year there is unused over-capacity, which is very expensive. Even between day and night there are big swings in power demand, as shown in Fig. 1 , requiring cycling of power equipment that is most efficiently run at a single optimum point at steady state.
Reversible fuel cells, also called "flow batteries", have been proposed as a way of effectively shaving off those peaks in demand thereby leveling the load on the grid. During peak-demand hours the cells would be run to deliver the needed power to the grid, consuming the fuel. During low-demand hours, electricity would be taken from the grid to run the cells backwards, thereby regenerating the fuel and getting it ready for the next peak. It may also make sense to install flow batteries in the bases of intermittent sources such as wind turbines.
The reason that hydrogen-halogen fuel cells (Fig. 2) have been proposed instead of hydrogen oxygen fuel cells for peak shaving / load leveling on the electrical grid is the inefficiencies associated with the oxygen electrode. Round-trip efficiencies of electric to electric energy conversion have not exceeded 50%. Years of research on the catalysis of oxygen reduction have not led to a solution. In contrast, halogen reduction seems to be significantly more reversible than oxygen reduction because the former is a one-electron process and the latter requires transferring two electrons at a single voltage1. If the voltage is chosen so the first electron goes reversibly, then the second electron is at either too low or too high a potential for reversible transfer.
We are particularly interested in developing the hydrogen-chlorine fuel cell because it is the component most in need of significant development in the House Process for mitigating global climate change by electrochemically accelerating chemical weathering. But there will be lots of synergies among R&D efforts on fuel cells using hydrogen and any halogen.
During the fall 2006 semester Jason Rugolo, who was a first year graduate student in applied physics, put together a rudimentary hydrogen-chlorine fuel cell, shown in Fig. 3. The proton conducting membrane and the gas diffusion electrodes were purchased from a supply house that sells parts only for hydrogen-oxygen fuel cells. He got current out of it before the reaction product, hydrochloric acid, caused enough problems that he had to shut it down. Clearly there is a lot of room for improvement.
First we need to see where the losses are. Jason has a new fuel cell design and is currently implementing it, still using off-the-shelf membranes and electrode assemblies. He is also building a testing station that will permit him to learn where the significant losses are. There are likely to be losses at the electrodes, ohmic losses within the membrane and the acid reservoir, and back-diffusion of chloride. Next, we plan to explore the potential for new materials and designs to improve efficiency, throughput, and lifetime. These will include advanced membranes, possibly including crystalline proton or chloride conductors; stable, high surface area catalysts; and improved engineering design to reduce parasitic electrochemical reactions.
1 Thomassen, M.; Borresen, B.; Hagen, G.; Tunold, R. J. Appl. Electrochem. 33 , 9 (2003).
Electrochemical Acceleration of Chemical Weathering for Mitigating Anthropogenic Climate Change
Nanoporous Materials Produced by Electrochemical Processes